Automated Test Equipment (ATE) refers to apparatus which performs tests on a semiconductor device, known as the Device Under Test (DUT). The DUT is physically connected to the ATE by a robotic machine called a handler or prober and through a customized Interface Test Adapter or a “fixture” that adapts the ATE's test resources to the DUT.
Several of the available ATE for testing integrated circuits (ICs) have the capability to test analog to digital converters (ADCs). For example, the Teradyne/Eagle ETS-364 (Teradyne, Inc., North Reading, Mass.) can test ADCs. The all codes Ramp/Histogram method is generally used for testing ADCs. For the all codes Ramp/Histogram method, the analog input stair-step voltage ramp to the ADC must be linear, accurate, and be provided as very small voltage steps. However, known ATE resources are not accurate enough (i.e. have sufficient linearity and resolution) to test more than 8 bit ADCs.
For example, a 12 bit ADC, with 30 divisions per one code (or hits per code) and a 5 V full scale voltage range, requires an input voltage resolution better than about 5V/(212)/30=40.7 μV. The accuracy of the ATE must be about at least 10 times better than this 40.7 μV resolution value (which equates to ≈4 μV resolution). However, the resolution of the ETS-364 Tester's various instruments is 80 μV, which is too coarse for 12 bit ADC testing. If the input voltage is not accurate enough, the tester will provide false results for the ADC. What is needed is a source of a linear, accurate and fine granularity stair-step voltage ramp for accurately testing devices including ADCs having 10 or more bits.